This invention relates to an overlock sewing machine with a threading mechanism for easily threading a looper.
A conventional under-looper extends horizontally under a sewing machine bed. A needle plate located right above the under-looper, and components located around the under-looper, obstruct and complicate the threading of the under-looper.
To facilitate the threading operation, a looper is proposed in Japan Published Unexamined Utility Model application No. S59-188078.A movable arm, at the tip of which is a thread guide, is mounted on a looper carriage. First, the arm is inclined under the sewing machine bed, then the thread guide is threaded. When the arm is raised, thread is delivered from the yarn guide to the looper.
An overlock sewing machine is proposed in Japan Published Unexamined Utility Model application No. S61-77964.A rotatable lever, at the tip of which is a looper, is connected to or disconnected from a looper carriage by using a knob. When the looper is threaded, the rotatable lever should be detached from the looper carriage using the knob, and the rotatable lever should be turned until the looper emerges from an opening of a sewing machine frame.
However, in these prior-art machines, the looper must be threaded below the sewing machine bed. An operator must look into the sewing machine bed, and thread the looper, which is located near the bottom of the sewing machine. If the operator forgets to raise the arm and starts the sewing machine, the thread would slacken and a neat stitch could not be formed.
In the latter prior art, Japan Published Unexamined Utility Model application No. S61-77964,the threading operation is complicated. For example, the rotatable lever must be turned aside, and the position of the rotatable lever must be adjusted by loosening and tightening the knob.